<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>高与宽</title>
    <style>
        .c1 {
            height: 300px;
            width: 500px;
        }
        .c2 {
            height: 300px;
            width: 50%;
        }
        .c3{
            height: 300px;
            width: 500px;
        }
    </style>
</head>
<body>
<div class="c1">Aa</div>
<div class="c2">Bb</div>
<span class="c3">Cc</span>
</body>
</html>